The present invention relates to an oil-impregnated capacitor. More particularly, it is concerned with a capacitor impregnated with aromatic hydrocarbons which contains 1-phenyl-1-methylphenylethane having a specific isomer ratio.
Heretofore there has been a keen demand for the reduction in size and increase in voltage of an oil-impregnated capacitor and various improvements have been made for electrical insulating materials which constitute an oil-impregnated capacitor, i.e., an impregnating electrical insulating oil and a dielectric.
For example, in British Pat. No.2032950 there is proposed an oil-impregnated capacitor impregnated with 1-phenyl-1-methylphenylethane. This oil-impregnated capacitor can somewhat satisfy the demand for the reduction in size and increase in voltage. But a further improvement has been desired. In this connection, it has recently been required for an oil-impregnated capacitor to have a low temperature characteristic; that is, an oil-impregnated capacitor is required to be capable of fully fulfilling its performance without breakdown even under application of a high voltage at a low temperature, for example, about -50.degree. C. But the low temperature characteristic of the above-proposed oil-impregnated capacitor is not always satisfactory.
As the measure of improvement of the capacitor performance, a corona discharge start voltage (CSV) or a corona discharge extinction voltage (CEV) is measured, for example. However, the breakdown phenomenon of an oil-impregnated capacitor is extremely complex and difficult to clarify because of an interaction in affinity or permeability between an insulating oil and a dielectric under a high voltage in addition to the complexity peculiar to the breakdown phenomenon. Therefore, CSV or CEV cannot serve as the measure of the capacitor performance. The most reliable method is to actually prepare an oil-impregnated capacitor and measure its life. The improvement of the performance of an oil-impregnated capacitor must therefore be done in such a manner.